The invention disclosed herein pertains to the field of map making and more particularly to a method for the representation of relief on a conventional two dimensional map to provide thereon the simulation of a third dimension and to the map produced thereby. Most features are readily shown on maps either by drawing them to scale, or arbitrarily out of scale, and by the use of conventional map maker symbols or other such means; however, the showing of relief, such as by shade to reflect slope, offers a peculiar problem because it involves the third dimension, that is the dimension of depth in addition to those of length and breadth.
One of the earliest and most simple methods developed in the art of map making to represent relief on maps is the process of determining the altitude and location of a particular point and marking it on the map. While spot marking alone fails to give any general idea of relief, it is helpful in revealing the height of hill summits or points along a road. A more complex method contemplates the use of contours, whereby lines having a constant height above sea-level or a known reference point are used as a means of showing relief. Both spot marking and contours provide an exact method of representing relief on a map; however, neither illustrate visually the effect of elevations and depressions to provide the map with the simulation of depth.
While methods have been developed in the prior art to pictorially represent relief on a map, primarily in some form of shade relief, each, however, has heretofore failed to provide a shade relief map sufficiently simple and inexpensive in manufacture to enable distribution thereof on a wide scale, yet a map having sufficiently accurate representation of relief thereon so that such representations might be useful for purposes other than mere decoration and/or ornamentation.
One method, long known in the art, for pictorial representation of relief makes use of shade to bring out the relief on a map. The shading, or stippling as it is sometimes called, is executed manually with a stubby brush, with the purpose of bringing out relief as it would be seen on a three-dimensional relief model lighted from above. The flat parts appear light and the slopes rather darker. While a shade relief map produced by stippling is similar to the map made by the novel method of this invention, disadvantages of the known method reside in the fact that it is manually executed, thereby lacking in the accuracy and exactness of the present invention, and, moreover, represents considerable commitment of time and money in obtaining the requisite artisan skills to visually and manually convert relief data into a shade-type pictoral representation of relief useful in map production.
Finally, a shadow effect for representing relief is attained by stippling a map to represent relief as it would appear if the area were lighted from the north-west corner. This effect, which is, perhaps, the most common process for making relief maps, is also accomplished by the construction of a three-dimensional model from plaster of Paris or the like, then photographing the model with oblique lighting whereby shadows are cast to provide the effect of an aerial photograph wherein the shadows are projected toward the observer. See, for example, U.S. Pat. No. 3,078,598. The effect of this method is not always sound. First, because an escarpment facing the north-west is not brought out at all, while the one facing the south-east is seen by the representation of shadow. Finally, upon viewing a map having shadow related relief without properly orientating it to the viewer, distortions in the form opposite those intended result. For example, a railroad fill instead appears as a cut, rivers and streams will appear to run along the tops of hills and ridges, rather than along valleys and cuts.
Accordingly, the whole difficulty of showing relief by a uniform method which would render comparison of areas easy resides in the fact that one method ideal for a region of high relief is unsuited to a region of low relief. Therefore, for the representation of all types of topography in the production of maps in a national survey, some sort of compromise has heretofore been necessary in the selection of a single known method or combination thereof.